1. Field of the Invention
The invention relates to composite piles and, more particularly, to a composite pile in which a transition fitting is fitted telescopically to the end of a shell.
2. Description of the Prior Art
A typical composite pile includes a wooden section driven deep into the earth and a tubular steel shell secured to the top of the wooden section. The tubular shell extends upwardly to the vicinity of the surface of the earth. The shell is filled with concrete to provide an assembly which provides support on which a building or other structure may be assembled.
There are at least two types of composite piles. One type uses corrugated steel shells while another uses smooth-walled pipe as a form for the concrete. In many applications a corrugated shell is preferred, if for no other reason, because of cost.
A problem in prior corrugated type composite piles is the manner in which the corrugated shell is secured to the wooden section. In most piles, a so-called transition fitting is secured to one end of the shell, such as by butt welding the end of the shell to an annular plate at or near the top of the transition fitting. The transition fitting is driven into the wooden section after the wooden section itself has been driven to a point where the top of the wooden section is at or near ground level. Repeated blows from the driving mechanism force the wooden section and the now-attached shell into the earth to the desired depth.
Since the corrugated shell has relatively little compressive strength, the pile is driven with an elongated mandrel that acts against the transition fitting and the wood section. Thus, the corrugated shell is literally pulled into the earth through its connection to the transition fitting. In prior corrugated shell composite piles, this connection has been accomplished by a weld connection between the transition fitting and the shell at a location above the pile. Since there are tremendous frictional forces between the shell and the surrounding earth, substantial tensile forces are imposed on the weld. In addition, the frictional forces tend to elongate the relatively thin-walled shell and this elongation tends to reduce the diameter of the shell. This size reduction causes a shear force to be applied to the weld as well as the tensile force.
Unless the weld is substantially perfect, there is a great potential for weld failure and as a consequence for a failure to construct a satisfactory pile because the wood and transition fitting will separate from the shell. While there has been a proposal to use a smooth walled pipe in a tenon arrangement, and to drive the shell along with a transition fitting into the piling, the corrugated shell itself has in the past always been connected to a transition fitting with an exposed weld above the wood pile.